Version: XState v4

@xstate/graph

The @xstate/graph package contains graph algorithms and utilities for XState machines.

Quick start

Install xstate and @xstate/graph:

npm install xstate @xstate/graph

Import the graph utilities. Example:

import { createMachine } from 'xstate';
import { getSimplePaths } from '@xstate/graph';

const machine = createMachine(/* ... */);
const paths = getSimplePaths(machine);

API

`getShortestPaths(machine, options?)`

Arguments

machine - the Machine to traverse
options (optional) - options that customize how the algorithm will traverse the machine

Returns the shortest paths (Dijkstra's algorithm) of a machine from the initial state to every other state as a mapped object, where the:

key is the stringified state
value is an object with the properties:
- state - the target State
- path - the shortest path to get from the initial state to the target state

The path is an array of segments, where each segment is an object with the properties:

state - the State of the segment
weight - the total weight of the path
- Currently, each transition from one state to another has a weight of 1. This will be customizable in the future.
event - the event object that transitions the machine from the state to the next state in the path

Every path starts with the initial state.

The overall object structure looks like this:

{
  "<SERIALIZED STATE>": {
    "state": State { ... },
    "path": [
      {
        "state": State { ... },
        "event": { "type": "<event.type>", "<PROP>": "<event.PROP>" }
      },
      {
        "state": State { ... },
        "event": { "type": "<event.type>", "<PROP>": "<event.PROP>" }
      },
      ...
    ]
  },
  ...
}

Example

import { createMachine } from 'xstate';
import { getShortestPaths } from '@xstate/graph';

const feedbackMachine = createMachine({
  id: 'feedback',
  initial: 'question',
  states: {
    question: {
      on: {
        CLICK_GOOD: 'thanks',
        CLICK_BAD: 'form',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    form: {
      on: {
        SUBMIT: 'thanks',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    thanks: {
      on: {
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    closed: {
      type: 'final',
    },
  },
});

const shortestPaths = getShortestPaths(feedbackMachine);

console.log(shortestPaths);
// => {
//   '"question"': {
//     state: State { value: 'question', context: undefined },
//     weight: 0,
//     path: []
//   },
//   '"thanks"': {
//     state: State { value: 'thanks', context: undefined },
//     weight: 1,
//     path: [
//       {
//         state: State { value: 'question', context: undefined },
//         event: { type: 'CLICK_GOOD' }
//       }
//     ]
//   },
//   '"form"': {
//     state: State { value: 'form', context: undefined },
//     weight: 1,
//     path: [
//       {
//         state: State { value: 'question', context: undefined },
//         event: { type: 'CLICK_BAD' }
//       }
//     ]
//   },
//   '"closed"': {
//     state: State { value: 'closed', context: undefined },
//     weight: 1,
//     path: [
//       {
//         state: State { value: 'question', context: undefined },
//         event: { type: 'CLOSE' }
//       }
//     ]
//   }
// };

`getSimplePaths(machine, options?)`

Arguments:

machine - the Machine to traverse
options (optional) - options that customize how the algorithm will traverse the machine

Returns the simple paths of a machine as a mapped object, where the:

key is the stringified state
value is an object with the properties:
- state - the target State
- paths - the array of paths to get from the initial state to the target state

Each path in paths is an array of segments, where each segment of the path is an object with the properties:

state - the State of the segment
event - the event object that transitions the machine from the state to the next state in the path

Every path starts with the initial state.

The overall object structure looks like this:

{
  "<SERIALIZED STATE>": {
    "state": State { ... },
    "paths": [
      [
        {
          "state": State { ... },
          "event": { "type": "<event.type>", "<PROP>": "<event.PROP>" }
        },
        {
          "state": State { ... },
          "event": { "type": "<event.type>", "<PROP>": "<event.PROP>" }
        },
        ...
      ],
      ...
    ]
  },
  ...
}

Example

import { createMachine } from 'xstate';
import { getSimplePaths } from '@xstate/graph';

const feedbackMachine = createMachine({
  id: 'feedback',
  initial: 'question',
  states: {
    question: {
      on: {
        CLICK_GOOD: 'thanks',
        CLICK_BAD: 'form',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    form: {
      on: {
        SUBMIT: 'thanks',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    thanks: {
      on: {
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    closed: {
      type: 'final',
    },
  },
});

const simplePaths = getSimplePaths(feedbackMachine);

console.log(simplePaths);
// => {
//   '"question"': {
//     state: { value: 'question', context: undefined },
//     paths: [[]]
//   },
//   '"thanks"': {
//     state: { value: 'thanks', context: undefined },
//     paths: [
//       [
//         {
//           state: { value: 'question', context: undefined },
//           event: { type: 'CLICK_GOOD' }
//         }
//       ],
//       [
//         {
//           state: { value: 'question', context: undefined },
//           event: { type: 'CLICK_BAD' }
//         },
//         {
//           state: { value: 'form', context: undefined },
//           event: { type: 'SUBMIT' }
//         }
//       ]
//     ]
//   },
//   '"closed"': {
//     state: { value: 'closed', context: undefined },
//     paths: [
//       [
//         {
//           state: { value: 'question', context: undefined },
//           event: { type: 'CLICK_GOOD' }
//         },
//         {
//           state: { value: 'thanks', context: undefined },
//           event: { type: 'CLOSE' }
//         }
//       ],
//       [
//         {
//           state: { value: 'question', context: undefined },
//           event: { type: 'CLICK_GOOD' }
//         },
//         {
//           state: { value: 'thanks', context: undefined },
//           event: { type: 'ESC' }
//         }
//       ],
//       ...
//     ]
//   },
//   ...
// };

`getPathFromEvents(machine, events)`

Arguments:

machine - the Machine to traverse
events - the sequence of events to generate a path from

Returns a path object with the following keys:

state - the target State
segments - an array of objects with the following shape:
- state - the State of the segment
- event - the event object that transitions the machine from the state to the next state in the path

import { createMachine } from 'xstate';
import { getSimplePaths } from '@xstate/graph';

const feedbackMachine = createMachine({
  id: 'feedback',
  initial: 'question',
  states: {
    question: {
      on: {
        CLICK_GOOD: 'thanks',
        CLICK_BAD: 'form',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    form: {
      on: {
        SUBMIT: 'thanks',
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    thanks: {
      on: {
        CLOSE: 'closed',
        ESC: 'closed',
      },
    },
    closed: {
      type: 'final',
    },
  },
});

const path = getPathFromEvents(feedbackMachine, [
  { type: 'CLICK_GOOD' },
  { type: 'SUBMIT' },
  { type: 'CLOSE' },
]);

console.log(path);
// => {
//   state: { value: 'closed' },
//   segments: [
//     {
//       state: { value: 'question' },
//       event: { type: 'CLICK_GOOD' },
//     },
//     {
//       state: { value: 'form' },
//       event: { type: 'SUBMIT' },
//     },
//     {
//       state: { value: 'thanks' },
//       event: { type: 'CLOSE' },
//     },
//   ],
// }

`toDirectedGraph(machine)`

Converts a machine to a directed graph structure.

Argument	Type	Description
`machine`	XState Machine created by `createMachine(...)`	The machine to convert to a directed graph structure

Example

import { toDirectedGraph } from '@xstate/graph';

const machine = createMachine({/* ... */});

const digraph = toDirectedGraph(machine);

// returns an object with this structure:
{
  id: '...',
  stateNode: /* StateNode */,
  children: [
    { id: '...', children: [/* ... */], edges: [/* ... */] },
    { id: '...', /* ... */ },
    // ...
  ],
  edges: [
    { source: /* ... */, target: /* ... */, transition: /* ... */ }
    // ...
  ]
}

Options

Options can be passed into getShortestPaths or getSimplePaths to customize how the graph represented by the machine should be traversed:

events - a mapping of event types to an array of event objects to be used for those events
filter - a function that determines whether a state should be traversed. If false, the traversal algorithm(s) will assume the state was "seen" and ignore traversing it.

Examples

In the below example, the INC event is expanded to include two possible events, with value: 1 and value: 2 as the payload. It also ensures that the state.context.count <= 5; otherwise, this machine would be traversed infinitely.

const counterMachine = createMachine({
  id: 'counter',
  initial: 'active',
  context: { count: 0 },
  states: {
    active: {
      on: {
        INC: {
          actions: assign({ count: (ctx, e) => ctx.count + e.value }),
        },
      },
    },
  },
});

const shortestPaths = getShortestPaths(counterMachine, {
  events: {
    INC: [
      { type: 'INC', value: 1 },
      { type: 'INC', value: 2 },
    ],
  },
  filter: (state) => state.context.count <= 5,
});

console.log(shortestPaths);
// => {
//   '"active" | {"count":0}': {
//     state: { value: 'active', context: { count: 0 } },
//     weight: 0,
//     path: []
//   },
//   '"active" | {"count":1}': {
//     state: { value: 'active', context: { count: 1 } },
//     weight: 1,
//     path: [
//       {
//         state: { value: 'active', context: { count: 0 } },
//         event: { type: 'INC', value: 1 }
//       }
//     ]
//   },
//   '"active" | {"count":2}': {
//     state: { value: 'active', context: { count: 2 } },
//     weight: 1,
//     path: [
//       {
//         state: { value: 'active', context: { count: 0 } },
//         event: { type: 'INC', value: 2 }
//       }
//     ]
//   },
//   '"active" | {"count":3}': {
//     state: { value: 'active', context: { count: 3 } },
//     weight: 2,
//     path: [
//       {
//         state: { value: 'active', context: { count: 0 } },
//         event: { type: 'INC', value: 1 }
//       },
//       {
//         state: { value: 'active', context: { count: 1 } },
//         event: { type: 'INC', value: 2 }
//       }
//     ]
//   },
//   ...
// };

Quick start​

API​

getShortestPaths(machine, options?)​

Arguments​

Example​

getSimplePaths(machine, options?)​

Example​

getPathFromEvents(machine, events)​

toDirectedGraph(machine)​

Example​

Options​

Examples​

Quick start

API

`getShortestPaths(machine, options?)`

Arguments

Example

`getSimplePaths(machine, options?)`

Example

`getPathFromEvents(machine, events)`

`toDirectedGraph(machine)`

Example

Options

Examples